Playback apparatus and method, and recording medium

ABSTRACT

At a step S 2 , a defect period monitoring unit of a defect processing control unit stands by until the defect period monitoring unit detects the start of a defect period. When the defect period monitoring unit detects the start of a defect period, the processing proceeds to a step S 3 . At the step S 3 , defect period processing is performed. When the defect period monitoring unit detects the end of the defect period at a step S 4 , the processing proceeds to a step S 5 . At the step S 5 , post-defect period processing is performed.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to an apparatus and a method forplayback and a recording medium, and particularly to an apparatus and amethod for playback and a recording medium suitable for use inpreventing a malfunction of a servo of an optical pickup resulting froma flaw or the like on a disk medium, for example.

[0002]FIG. 1 shows a configuration of a conventional optical diskplayback apparatus for reproducing data recorded on an optical disk.

[0003] A spindle motor 2 in the conventional optical disk playbackapparatus drives and rotates an optical disk 1. An optical pickup 3irradiates the optical disk 1 with laser light, generates a signalcorresponding to the reflected light, and then outputs the signal to anRF signal generating unit 4, an FE signal generating unit 5, and a TEsignal generating unit 6. Also, the optical pickup 3 adjusts focus servooperation in response to a focus drive signal from a focus driver 10,and adjusts tracking servo operation in response to a tracking drivesignal from a tracking driver 12.

[0004] The RF signal generating unit 4 generates an RF signal on thebasis of the signal from the optical pickup 3, and then outputs the RFsignal to a binarizing unit 7 and a defect detecting unit 8. The FEsignal generating unit 5 generates a focus error signal (hereinafterdescribed as an FE signal) on the basis of the signal from the opticalpickup 3, and then outputs the FE signal to a focus servo control unit9. The TE signal generating unit 6 generates a tracking error signal(hereinafter described as a TE signal) on the basis of the signal fromthe optical pickup 3, and then outputs the TE signal to a tracking servocontrol unit 11.

[0005] The binarizing unit 7 generates a data signal by binarizing theRF signal from the RF signal generating unit 4 into 0 or 1. The defectdetecting unit 8 detects a loss of a signal (defect) resulting from aflaw, a stain or the like present on the optical disk 1 on the basis ofthe RF signal from the RF signal generating unit 4, generates a defectsignal indicating a period of a defect detected, and then outputs thedefect signal to the focus servo control unit 9 and the tracking servocontrol unit 11.

[0006] A method for detecting a defect is, for example, to set level ofthe defect signal during a period when level of the RF signal is lowerthan a predetermined threshold value as High, and to set the defectsignal during a period when the level of the RF signal is higher thanthe predetermined threshold value as Low. Specifically, when the RFsignal has a level as shown in FIG. 2A, the defect signal has acorresponding level as shown in FIG. 2B.

[0007] During a normal period (period when the level of the defectsignal from the defect detecting unit 8 is Low), the focus servo controlunit 9 generates a focus drive control signal corresponding to the FEsignal from the FE signal generating unit 5, and then outputs the focusdrive control signal to the focus driver 10. When the level of thedefect signal is High, the focus servo control unit 9 holds level of thefocus drive control signal at a predetermined reference value or a valueof the focus drive control signal immediately before the level of thedefect signal becomes High, as shown in FIG. 2D, and then outputs thelevel of the focus drive control signal to the focus driver 10.

[0008] The focus driver 10 generates a focus drive signal correspondingto the focus drive control signal from the focus servo control unit 9,and then outputs the focus drive signal to the optical pickup 3.

[0009] During a normal period (period when the level of the defectsignal from the defect detecting unit 8 is Low), the tracking servocontrol unit 11 generates a tracking drive control signal on the basisof the TE signal from the TE signal generating unit 6, and then outputsthe tracking drive control signal to the tracking driver 12. When thelevel of the defect signal is High, the tracking servo control unit 11holds level of the tracking drive control signal at a predeterminedreference value or a value of the tracking drive control signalimmediately before the level of the defect signal becomes High, as shownin FIG. 2F, and then outputs the level of the tracking drive controlsignal to the tracking driver 12.

[0010] The tracking driver 12 generates a tracking drive signalcorresponding to the tracking drive control signal from the trackingservo control unit 11, and then outputs the tracking drive signal to theoptical pickup 3.

[0011] In some cases, the conventional optical disk playback apparatussupplies the defect signal generated by the defect detecting unit 8 tothe FE signal generating unit 5 and the TE signal generating unit 6.

[0012] In such cases, during a normal period (period when the level ofthe defect signal from the defect detecting unit 8 is Low), the FEsignal generating unit 5 supplied with the defect signal generates theFE signal on the basis of the signal from the optical pickup 3, and thenoutputs the FE signal to the focus servo control unit 9. When the levelof the defect signal is High, the FE signal generating unit 5 holdslevel of the FE signal at a predetermined reference value or a value ofthe FE signal immediately before the level of the defect signal becomesHigh, as shown in FIG. 2C, and then outputs the level of the FE signalto the focus servo control unit 9. The focus servo control unit 9outputs a focus drive signal as shown in FIG. 2D corresponding to the FEsignal whose level is being held constant.

[0013] During a normal period (period when the level of the defectsignal from the defect detecting unit 8 is Low), the TE signalgenerating unit 6 supplied with the defect signal generates the TEsignal on the basis of the signal from the optical pickup 3, and thenoutputs the TE signal to the tracking servo control unit 11. When thelevel of the defect signal is High, the TE signal generating unit 6holds level of the TE signal at a predetermined reference value or avalue of the TE signal immediately before the level of the defect signalbecomes High, as shown in FIG. 2E, and then outputs the level of the TEsignal to the tracking servo control unit 11. The tracking servo controlunit 11 outputs a tracking drive signal as shown in FIG. 2Fcorresponding to the TE signal having a fixed value.

[0014] Thus, even if normal reflected light is not obtained because ofthe presence of a flaw or the like on the optical disk 1, theconventional optical disk playback apparatus thus formed holds the levelof the focus drive signal and the tracking drive signal while the levelof the defect signal is High. Therefore, a malfunction of a focus servoand a tracking servo of the optical pickup 3 is prevented.

[0015] However, in the case of a long High-level period of the defectsignal or depending on an error in the output of the held focus drivesignal and tracking drive signal, the optical pickup 3 is displacedsubstantially from an original servo control position when the level ofthe defect signal returns to Low.

[0016] Japanese Patent Laid-Open No. Sho 59-203276, for example,discloses a method for preventing such displacement which, directingattention to characteristics of the TE signal such as periodicity,generates a pseudo error signal approximating an original TE signal bycalculation using a tracking error and a track period, and uses thecalculated pseudo error signal instead of the original TE signal whilethe level of the defect signal is High.

[0017] Also, Japanese Patent Laid-Open No. Sho 64-39638 discloses amethod which changes focus offset adjusting voltage to a predeterminedvalue to thereby prevent displacement of a focus coil while the level ofthe defect signal is High, and thus minimizes the error when the levelof the defect signal returns to Low.

[0018] The conventional techniques described above are all principallyaimed to reduce a range of the control error while the level of thedefect signal is High and after the level of the defect signal returnsto Low, and give no consideration to reduction of a period from thereturn to Low of the level of the defect signal to the return to anormal control state of the servo.

[0019] In general, as the High-level period of the defect signal becomeslonger, the control error tends to be increased. Hence, in case wherethe control error is large if not departing from a normal servo controlrange when the level of the defect signal returns to Low, for example,as shown in FIGS. 3A, 3B, 3C, 3D, and 3E, the servo continues to beunstable and requires considerable time before the servo returns to anormal control state.

[0020] In order to return the servo quickly to the normal control state,there is known a method which maintains a servo loop gain at ahigher-than-normal level immediately after a track jump or the like.However, when the servo loop gain is high, the servo is generally toosensitive to a defect such as a flaw on the optical disk. Therefore, themethod of increasing the servo loop gain cannot be used to improvedefect passage characteristics.

SUMMARY OF THE INVENTION

[0021] The present invention has been made in view of the above, and itis accordingly an object of the present invention to reduce timerequired for the servo to return to the normal control state after thelevel of the defect signal returns to Low.

[0022] According to the present invention, there is provided a playbackapparatus comprising: RF signal generating means for generating an RFsignal on the basis of an analog signal outputted by an optical pickup;data signal generating means for generating a data signal by binarizingthe RF signal; defect signal generating means for generating a defectsignal for indicating a defect on a disk medium on the basis of the RFsignal; focus error signal generating means for generating a focus errorsignal on the basis of the analog signal outputted by the opticalpickup; a focus servo control means for controlling a focus servo of theoptical pickup in response to the focus error signal; tracking errorsignal generating means for generating a tracking error signal on thebasis of the analog signal outputted by the optical pickup; trackingservo control means for controlling a tracking servo of the opticalpickup in response to the tracking error signal; monitoring means formonitoring the defect signal and thereby detecting a start and an end ofa defect period; defect period processing control means for controllingthe focus servo control means and the tracking servo control means sothat the focus servo control means and the tracking servo control meansperform defect period processing when a result of the monitoring by themonitoring means indicates the defect period; and post-defect periodprocessing control means for controlling the focus servo control meansand the tracking servo control means so that the focus servo controlmeans and the tracking servo control means perform post-defect periodprocessing when a result of the monitoring by the monitoring meansindicates the end of the defect period.

[0023] The defect period processing control means can control the focusservo control means and the tracking servo control means so that thefocus error signal or the tracking error signal of the optical pickup isheld at a predetermined value.

[0024] The post-defect period processing control means can control thefocus servo control means and the tracking servo control means so thatservo operation of the optical pickup is sped up.

[0025] When the monitoring means detects the start of the defect periodduring the post-defect period processing performed under control of thepost-defect period processing control means, the post-defect periodprocessing control means can stop the post-defect period processing, andthe defect period processing control means can start the defect periodprocessing.

[0026] According to the present invention, there is provided a playbackmethod comprising: an RF signal generating step for generating an RFsignal on the basis of an analog signal outputted by an optical pickup;a data signal generating step for generating a data signal by binarizingthe RF signal; a defect signal generating step for generating a defectsignal for indicating a defect on a disk medium on the basis of the RFsignal; a focus error signal generating step for generating a focuserror signal on the basis of the analog signal outputted by the opticalpickup; a focus servo control step for controlling a focus servo of theoptical pickup in response to the focus error signal; a tracking errorsignal generating step for generating a tracking error signal on thebasis of the analog signal outputted by the optical pickup; a trackingservo control step for controlling a tracking servo of the opticalpickup in response to the tracking error signal; a monitoring step formonitoring the defect signal and thereby detecting a start and an end ofa defect period; a defect period processing control step for controllingprocessing of the focus servo control step and processing of thetracking servo control step so that defect period processing isperformed when a result of the monitoring by processing of themonitoring step indicates the defect period; and a post-defect periodprocessing control step for controlling the processing of the focusservo control step and the processing of the tracking servo control stepso that post-defect period processing is performed when a result of themonitoring by the processing of the monitoring step indicates the end ofthe defect period.

[0027] According to the present invention, there is provided a programon a recording medium, comprising: an RF signal generating step forgenerating an RF signal on the basis of an analog signal outputted by anoptical pickup; a data signal generating step for generating a datasignal by binarizing the RF signal; a defect signal generating step forgenerating a defect signal for indicating a defect on a disk medium onthe basis of the RF signal; a focus error signal generating step forgenerating a focus error signal on the basis of the analog signaloutputted by the optical pickup; a focus servo control step forcontrolling a focus servo of the optical pickup in response to the focuserror signal; a tracking error signal generating step for generating atracking error signal on the basis of the analog signal outputted by theoptical pickup; a tracking servo control step for controlling a trackingservo of the optical pickup in response to the tracking error signal; amonitoring step for monitoring the defect signal and thereby detecting astart and an end of a defect period; a defect period processing controlstep for controlling processing of the focus servo control step andprocessing of the tracking servo control step so that defect periodprocessing is performed when a result of the monitoring by processing ofthe monitoring step indicates the defect period; and a post-defectperiod processing control step for controlling the processing of thefocus servo control step and the processing of the tracking servocontrol step so that post-defect period processing is performed when aresult of the monitoring by the processing of the monitoring stepindicates the end of the defect period.

[0028] The playback apparatus and method and the program on a recordingmedium according to the present invention generate an RF signal on thebasis of an analog signal outputted by an optical pickup, generate adata signal by binarizing the RF signal, and generate a defect signalfor indicating a defect on a disk medium on the basis of the RF signal.Also, the playback apparatus and method and the program on a recordingmedium according to the present invention generate a focus error signalon the basis of the analog signal outputted by the optical pickup, andcontrol a focus servo of the optical pickup in response to the focuserror signal. In addition, the playback apparatus and method and theprogram on a recording medium according to the present inventiongenerate a tracking error signal on the basis of the analog signaloutputted by the optical pickup, and control a tracking servo of theoptical pickup in response to the tracking error signal. Furthermore,the playback apparatus and method and the program on a recording mediumaccording to the present invention detect a start and an end of a defectperiod by monitoring the defect signal, perform defect period processingwhen a result of the monitoring indicates the defect period, and performpost-defect period processing when a result of the monitoring indicatesthe end of the defect period.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029]FIG. 1 is a block diagram showing a configuration of aconventional optical disk playback apparatus;

[0030]FIGS. 2A, 2B, 2C, 2D, 2E, and 2F are diagrams of assistance inexplaining conventional processing for handling a defect;

[0031]FIGS. 3A, 3B, 3C, 3D, and 3E are diagrams of assistance inexplaining conventional processing for handling a defect;

[0032]FIG. 4 is a block diagram showing a configuration of an opticaldisk playback apparatus according to an embodiment of the presentinvention;

[0033]FIG. 5 is a flowchart of assistance in explaining defect handlingprocessing by the optical disk playback apparatus;

[0034]FIGS. 6A, 6B, 6C, 6D, and 6E are diagrams of assistance inexplaining defect handling processing by the optical disk playbackapparatus;

[0035]FIGS. 7A, 7B, 7C, 7D, and 7E are diagrams of assistance inexplaining defect handling processing by the optical disk playbackapparatus;

[0036]FIGS. 8A, 8B, 8C, 8D, and 8E are diagrams of assistance inexplaining defect handling processing by the optical disk playbackapparatus;

[0037]FIGS. 9A, 9B, 9C, 9D, and 9E are diagrams of assistance inexplaining defect handling processing by the optical disk playbackapparatus;

[0038]FIGS. 10A, 10B, 10C, 10D, and 10E are diagrams of assistance inexplaining defect handling processing by the optical disk playbackapparatus; and

[0039]FIGS. 11A, 11B, 11C, 11D, and 11E are diagrams of assistance inexplaining defect handling processing by the optical disk playbackapparatus.

DETAILED DESCRIPTION OF THE PREFFERED EMBODIMENTS

[0040] An example of configuration of an optical disk playback apparatusto which the present invention is applied will be described withreference to FIG. 4.

[0041] A spindle motor 22 forming the optical disk playback apparatus 20drives and rotates an optical disk 21. An optical pickup 23 irradiatesthe optical disk 21 with laser light, generates a signal correspondingto the reflected light, and then outputs the signal to an RF signalgenerating unit 24, an FE signal generating unit 25, and a TE signalgenerating unit 26. Also, the optical pickup 23 adjusts focus servooperation in response to a focus drive signal from a focus driver 39,and adjusts tracking servo operation in response to a tracking drivesignal from a tracking driver 46.

[0042] The RF signal generating unit 24 generates an RF signalcorresponding to the signal from the optical pickup 23, and then outputsthe RF signal to a binarizing unit 27 and a defect processing controlunit 28. The FE signal generating unit 25 generates an FE signal on thebasis of the signal from the optical pickup 23, and then outputs the FEsignal to a focus servo control unit 33. The TE signal generating unit26 generates a TE signal on the basis of the signal from the opticalpickup 23, and then outputs the TE signal to a tracking servo controlunit 40.

[0043] The binarizing unit 27 converts the RF signal from the RF signalgenerating unit 24 into digital data of 0 or 1, thus generating a datasignal.

[0044] A defect detecting unit 29 forming the defect processing controlunit 28 detects a loss of a signal (defect) resulting from a flaw, astain or the like present on the optical disk 21 on the basis of aresult of comparison between level of the RF signal from the RF signalgenerating unit 24 and a predetermined threshold value, for example. Thedefect detecting unit 29 generates a defect signal that has a Low levelduring a normal period (not a period of a defect) and has a High levelduring a defect period. The defect detecting unit 29 outputs the defectsignal to a defect period monitoring unit 30.

[0045] The defect period monitoring unit 30 monitors the defect signalfrom the defect detecting unit 29. During a period in which the defectsignal has a High level, the defect period monitoring unit 30 generatesa defect period signal indicating the High level of the defect signal,and then outputs the defect period signal to a defect period processingcontrol unit 31. When the level of the defect signal has returned fromHigh to Low, the defect period monitoring unit 30 generates a defectperiod end signal indicating that the level of the defect signal hasreturned from High to Low, and then outputs the defect period end signalto a post-defect period processing control unit 32.

[0046] In response to the defect period signal from the defect periodmonitoring unit 30, the defect period processing control unit 31controls a pre-stage switch 34 and an FE signal previous value hold unit37 of the focus servo control unit 33, as well as a pre-stage switch 41and a TE signal previous value hold unit 44 of the tracking servocontrol unit 40.

[0047] In response to the defect period end signal from the defectperiod monitoring unit 30, the post-defect period processing controlunit 32 controls a post-stage switch 36 of the focus servo control unit33, as well as a post-stage switch 43 of the tracking servo control unit40.

[0048] In the focus servo control unit 33, the FE signal from the FEsignal generating unit 25 is supplied to the pre-stage switch 34, the FEsignal previous value hold unit 37, and a post-defect servo control unit38.

[0049] The pre-stage switch 34 performs switching under control of thedefect period processing control unit 31. When the pre-stage switch 34is turned to a terminal (a) side, the FE signal from the FE signalgenerating unit 25 is outputted to a normal servo loop filter unit 35.On the other hand, when the pre-stage switch 34 is turned to a terminal(b) side, an FE signal held by the FE signal previous value hold unit 37is outputted to the normal servo loop filter unit 35. Normally, thepre-stage switch 34 is turned to the terminal (a) side.

[0050] The normal servo loop filter unit 35 generates a focus drivecontrol signal by subjecting the FE signal inputted thereto via thepre-stage switch 34 to low-frequency boost processing, phasecompensation processing, low-pass filter processing and the like. Thenormal servo loop filter unit 35 then outputs the focus drive controlsignal to a terminal (b) side of the post-stage switch 36.

[0051] The post-stage switch 36 performs switching under control of thepost-defect period processing control unit 32. When the post-stageswitch 36 is turned to a terminal (a) side, a focus drive control signalfrom the post-defect servo control unit 38 is outputted to the focusdriver 39. On the other hand, when the post-stage switch 36 is turned toa terminal (b) side, the focus drive control signal from the normalservo loop filter unit 35 is outputted to the focus driver 39. Normally,the post-stage switch 36 is turned to the terminal (b) side.

[0052] Under control of the defect period processing control unit 31,the FE signal previous value hold unit 37 holds the level of the FEsignal from the FE signal generating unit 25, and then outputs the levelof the FE signal to the terminal (b) side of the pre-stage switch 34.

[0053] The post-defect servo control unit 38 generates a focus drivecontrol signal by subjecting the FE signal from the FE signal generatingunit 25 to gain increase processing in addition to the processing of thenormal servo loop filter unit 35. The post-defect servo control unit 38then outputs the focus drive control signal to the terminal (a) side ofthe post-stage switch 36.

[0054] The focus driver 39 generates a focus drive signal on the basisof the focus drive control signal from the post-stage switch 36, andthen outputs the focus drive signal to the optical pickup 23.

[0055] In the tracking servo control unit 40, the TE signal from the TEsignal generating unit 26 is supplied to the pre-stage switch 41, the TEsignal previous value hold unit 44, and a post-defect servo control unit45.

[0056] The pre-stage switch 41 performs switching under control of thedefect period processing control unit 31. When the pre-stage switch 41is turned to a terminal (a) side, the TE signal from the TE signalgenerating unit 26 is outputted to a normal servo loop filter unit 42.On the other hand, when the pre-stage switch 41 is turned to a terminal(b) side, a TE signal held by the TE signal previous value hold unit 44is outputted to the normal servo loop filter unit 42. Normally, thepre-stage switch 41 is turned to the terminal (a) side.

[0057] The normal servo loop filter unit 42 generates a tracking drivecontrol signal by subjecting the TE signal inputted thereto via thepre-stage switch 41 to low-frequency boost processing, phasecompensation processing, low-pass filter processing and the like. Thenormal servo loop filter unit 42 then outputs the tracking drive controlsignal to a terminal (b) side of the post-stage switch 43.

[0058] The post-stage switch 43 performs switching under control of thepost-defect period processing control unit 32. When the post-stageswitch 43 is turned to a terminal (a) side, a tracking drive controlsignal from the post-defect servo control unit 45 is outputted to thetracking driver 46. On the other hand, when the post-stage switch 43 isturned to a terminal (b) side, the tracking drive control signal fromthe normal servo loop filter unit 42 is outputted to the tracking driver46. Normally, the post-stage switch 43 is turned to the terminal (b)side.

[0059] Under control of the defect period processing control unit 31,the TE signal previous value hold unit 44 holds the level of the TEsignal from the TE signal generating unit 26, and then outputs the levelof the TE signal to the terminal (b) side of the pre-stage switch 41.

[0060] The post-defect servo control unit 45 generates a tracking drivecontrol signal by subjecting the TE signal from the TE signal generatingunit 26 to gain increase processing in addition to the processing of thenormal servo loop filter unit 42. The post-defect servo control unit 45then outputs the tracking drive control signal to the terminal (a) sideof the post-stage switch 43.

[0061] The tracking driver 46 generates a tracking drive signal on thebasis of the tracking drive control signal from the post-stage switch43, and then outputs the tracking drive signal to the optical pickup 23.

[0062] A control unit 50 controls a drive 51 to read a control programstored on a magnetic disk 52, an optical disk 53, a magneto-optical disk54, or a semiconductor memory 55, and then controls the whole of theoptical disk playback apparatus 20 on the basis of the read controlprogram.

[0063] Defect handling processing by the optical disk playback apparatus20 will next be described with reference to a flowchart of FIG. 5 andFIGS. 6A, 6B, 6C, 6D, and 6E. The defect handling processing is intendedto handle a loss of a signal (defect) resulting from a flaw, a stain orthe like present on the optical disk 21, and is started simultaneouslywith a start of processing of reproducing data from the optical disk 21.

[0064] At a step S1, the defect period processing control unit 31 of thedefect processing control unit 28 effects control to turn the pre-stageswitch 34 of the focus servo control unit 33 and the pre-stage switch 41of the tracking servo control unit 40 to the terminal (a) side, which isa normal position.

[0065] At a step S2, the defect period monitoring unit 30 of the defectprocessing control unit 28 monitors the defect signal from the defectdetecting unit 29 and stands by until the defect period monitoring unit30 detects the start of a defect period, that is, the defect periodmonitoring unit 30 detects a change in the level of the defect signalfrom Low to High, as shown in FIG. 6A. When the defect period monitoringunit 30 detects the start of a defect period (Td in FIG. 6A), theprocessing proceeds to a step S3.

[0066] At the step S3, the defect period monitoring unit 30 generates adefect period signal, and then outputs the defect period signal to thedefect period processing control unit 31. In response to the defectperiod signal from the defect period monitoring unit 30, the defectperiod processing control unit 31 controls the pre-stage switch 34 andthe FE signal previous value hold unit 37 of the focus servo controlunit 33, as well as the pre-stage switch 41 and the TE signal previousvalue hold unit 44 of the tracking servo control unit 40, as processingduring a defect period.

[0067] Under control of the defect period processing control unit 31,the FE signal previous value hold unit 37 holds the level of an FEsignal inputted from the FE signal generating unit 25 immediately beforethe defect period Td, as shown in FIG. 6B, and then outputs the level ofthe FE signal to the terminal (b) side of the pre-stage switch 34. TheTE signal previous value hold unit 44 holds the level of a TE signalinputted from the TE signal generating unit 26 immediately before thedefect period Td, as shown in FIG. 6D, and then outputs the level of theTE signal to the terminal (b) side of the pre-stage switch 41. Thepre-stage switches 34 and 41 are turned to the terminal (b) side.

[0068] At a step S4, the defect period monitoring unit 30 monitors thedefect signal from the defect detecting unit 29 and stands by until thedefect period monitoring unit 30 detects the end of the defect period,that is, the defect period monitoring unit 30 detects a change in thelevel of the defect signal from High to Low, as shown in FIG. 6A.

[0069] Thus, during the defect period Td, the FE signal held by the FEsignal previous value hold unit 37 is supplied to the normal servo loopfilter unit 35, while the TE signal held by the TE signal previous valuehold unit 44 is supplied to the normal servo loop filter unit 42.

[0070] Hence, during the defect period Td, the focus drive controlsignal generated by the normal servo loop filter unit 35 on the basis ofthe FE signal is also held constant, and accordingly the focus drivesignal generated by the focus driver 39 on the basis of the focus drivecontrol signal is also held constant, as shown in FIG. 6C. In addition,the tracking drive control signal generated by the normal servo loopfilter unit 42 on the basis of the TE signal is also held constant, andaccordingly the tracking drive signal generated by the tracking driver46 on the basis of the tracking drive control signal is also heldconstant, as shown in FIG. 6E.

[0071] Thus, during the defect period Td, a focus coil and a trackingcoil within the optical pickup 23 are held at a position immediatelybefore the defect period Td.

[0072] When the defect period monitoring unit 30 detects the end of thedefect period (Td in the figure) at the step S4, the processing proceedsto a step S5.

[0073] At the step S5, the defect period monitoring unit 30 generates adefect period end signal and then outputs the defect period end signalto the post-defect period processing control unit 32. In response to thedefect period end signal from the defect period monitoring unit 30, thepost-defect period processing control unit 32 controls the post-stageswitch 36 of the focus servo control unit 33, as well as the post-stageswitch 43 of the tracking servo control unit 40, as processing after thedefect period. Ta in FIGS. 6A, 6B, 6C, 6D, and 6E denotes a periodduring which the post-defect period processing is performed.

[0074] Under control of the post-defect period processing control unit32, the post-stage switches 36 and 43 are turned to the terminal (a)side. Thus, immediately after the defect period Td, a focus drivecontrol signal with an increased servo gain from the post-defect servocontrol unit 38 is supplied to the focus driver 39, while a trackingdrive control signal with an increased servo gain from the post-defectservo control unit 45 is supplied to the tracking driver 46.

[0075] At a step S6, the defect period monitoring unit 30 determineswhether the defect signal is brought into a defect state again. When thedefect period monitoring unit 30 determines that the defect signal isbrought into a defect state again, the post-defect period processing isstopped immediately, and the processing returns to the step S3 to repeatthe processes from the step S3 on down. When the defect periodmonitoring unit 30 determines at the step S6 that the defect signal isnot brought into a defect state again, the processing proceeds to a stepS7.

[0076] At the step S7, whether the post-defect period processing is tobe ended or not is determined on the basis of whether a predeterminedcondition (to be described later) is satisfied. The processing at thesteps S6 and S7 is repeated until it is determined that the post-defectperiod processing is to be ended. When it is determined at the step S7that the post-defect period processing is to be ended, the post-stageswitches 36 and 43 are turned to the terminal (b) side. Then, theprocessing returns to the step S2 to repeat the processes from the stepS2 on down.

[0077] The conditions for turning the post-stage switches 36 and 43 tothe terminal (b) side, that is, the conditions for timing of ending theperiod Ta are: passage of a predetermined time after turning thepost-stage switches 36 and 43 to the terminal (a) side; the passing of areference level by the FE signal and the TE signal; and reoccurrence ofa defect state. The post-stage switches 36 and 43 are turned to theterminal (b) side when one of the conditions is satisfied.

[0078] As described above, according to the defect handling processingby the optical disk playback apparatus 20, the post-defect periodprocessing, in which an action for correcting servo displacement isproduced more strongly than during a normal period (a period of nodefect), is started immediately after detection of the end of the defectperiod Td. Therefore, servo displacement can be corrected quickly ascompared with a case (FIGS. 3A, 3B, 3C, 3D, and 3E) where thepost-defect period processing is not performed.

[0079] Incidentally, the turning of the pre-stage switches 34 and 41while the post-defect period processing is performed at the step S5 isnot determined uniquely because the turning of the pre-stage switches 34and 41 is changed depending on the method of the post-defect periodprocessing and a situation in which a defect state occurs again.

[0080] The above-described operation of the post-defect servo controlunit 38 of the focus servo control unit 33 and the post-defect servocontrol unit 45 of the tracking servo control unit 40 will hereinafterbe described as first operation.

[0081] The post-defect servo control unit 38 of the focus servo controlunit 33 may detect a difference between the level of the FE signalimmediately after the end of the defect period and a reference level andoutput a pulse voltage acting to reduce the difference to the terminal(a) of the post-stage switch 36 as a focus drive control signal.

[0082] Similarly, the post-defect servo control unit 45 of the trackingservo control unit 40 may detect a difference between the level of theTE signal immediately after the end of the defect period and a referencelevel and output a pulse voltage acting to reduce the difference to theterminal (a) of the post-stage switch 43 as a tracking drive controlsignal. Such operation of the post-defect servo control units 38 and 45will hereinafter be described as second operation.

[0083] When the post-defect servo control units 38 and 45 perform thesecond operation, the condition for timing of returning the post-stageswitches 36 and 43 to the terminal (b) side, that is, the condition fortiming of ending the period Ta for performing the post-defect periodprocessing is the passing of a reference level by the FE signal and theTE signal.

[0084]FIGS. 7A, 7B, 7C, 7D, and 7E show a result of defect handlingprocessing when the post-defect servo control units 38 and 45 performthe second operation.

[0085]FIGS. 8A, 8B, 8C, 8D, and 8E show a result of processing when arelatively short defect occurs three times during the performance of thepost-defect period processing in which the post-defect servo controlunits 38 and 45 perform the first operation.

[0086]FIGS. 9A, 9B, 9C, 9D, and 9E show a result of processing when arelatively short defect occurs three times during the performance of thepost-defect period processing in which the post-defect servo controlunits 38 and 45 perform the second operation.

[0087] Since the servo is in a more unstable state during thepost-defect period processing than during normal operation, the level ofthe focus drive signal and the tracking drive signal held immediatelyafter reoccurrence of a defect state may not necessarily be appropriate.

[0088] Therefore, when a defect state occurs, output voltage of thefocus drive signal and the tracking drive signal may be fixed at areference level (for example zero potential) so that voltage is notapplied to the focus coil and the tracking coil.

[0089] In such a case, by resetting the length of the period Ta to aninitial value, it is possible to prevent the post-defect periodprocessing from being ended within less than a specified time. It isalso possible to deal with a case where a defect state continuallyoccurs in a short time.

[0090]FIGS. 10A, 10B, 10C, 10D, and 10E show a result of processingwhere the output voltage of the focus drive signal and the trackingdrive signal is set to be fixed at a reference level when a defect stateoccurs, and a relatively short defect occurs three times during theperformance of the post-defect period processing in which thepost-defect servo control units 38 and 45 perform the first operation.

[0091]FIGS. 11A, 11B, 11C, 11D, and 11E show a result of processingwhere the output voltage of the focus drive signal and the trackingdrive signal is set to be fixed at a reference level when a defect stateoccurs, and a relatively short defect occurs three times during theperformance of the post-defect period processing in which thepost-defect servo control units 38 and 45 perform the second operation.

[0092] As described above, the optical disk playback apparatus 20 towhich the present invention is applied monitors reoccurrence of adefect, and when a defect occurs, the optical disk playback apparatus 20stops the post-defect period processing to perform defect processingagain. Therefore, it is possible to solve the problem of the servobecoming too sensitive to a defect such as a flaw when the loop gain ofthe servo is increased, and it is thereby possible to make the servoless affected by a defect even when the servo loop gain is high.

[0093] It is to be noted that the present invention can be applied notonly to playback apparatus such as the present embodiment for playingback an optical disk such as a CD (Compact Disc) but also to playbackapparatus for playing back a DVD (Digital Versatile Disc), an MD (MiniDisc), a magneto-optical disk and the like.

[0094] The series of processing steps described above may be carried outnot only by hardware but also by software. When the series of processingsteps is to be carried out by software, a program is installed from arecording medium onto a computer where programs forming the software areincorporated in dedicated hardware, or a general-purpose personalcomputer that can perform various functions by installing variousprograms thereon, for example.

[0095] Examples of the recording medium include not onlyprogram-recorded package media distributed to users to provide theprogram separately from computers, such as the magnetic disks 52(including a floppy disk), the optical disks 53 (including CD-ROM(Compact Disk-Read Only Memory) and DVD (Digital Versatile Disk)), themagneto-optical disks 54 (including MD (Mini Disk)), or thesemiconductor memories 55, as shown in FIG. 4, but also a ROM and a harddisk storing the program and supplied to a user in a state of beingpreincorporated in a computer.

[0096] It is to be noted that in the present specification, the stepsdescribing the program recorded on a recording medium include not onlyprocessing steps carried out in time series in the described order butalso processing steps carried out in parallel or individually and notnecessarily in time series.

[0097] As described above, the playback apparatus and method and theprogram on a recording medium according to the present invention detectthe start and the end of a defect period by monitoring a defect signal,perform defect period processing when a result of the monitoringindicates a defect period, and perform post-defect period processingwhen a result of the monitoring indicates the end of the defect period.Therefore, it is possible to reduce time required for the servo of anoptical pickup to return to a normal control state after the end of adefect period.

What is claimed is:
 1. A playback apparatus for reproducing datarecorded on a disk medium by using an optical pickup, said playbackapparatus comprising: RF signal generating means for generating an RFsignal on the basis of an analog signal outputted by said opticalpickup; data signal generating means for generating a data signal bybinarizing said RF signal; defect signal generating means for generatinga defect signal for indicating a defect on said disk medium on the basisof said RF signal; focus error signal generating means for generating afocus error signal on the basis of said analog signal outputted by saidoptical pickup; focus servo control means for controlling a focus servoof said optical pickup in response to said focus error signal; trackingerror signal generating means for generating a tracking error signal onthe basis of said analog signal outputted by said optical pickup;tracking servo control means for controlling a tracking servo of saidoptical pickup in response to said tracking error signal; monitoringmeans for monitoring said defect signal and thereby detecting a startand an end of a defect period; defect period processing control meansfor controlling said focus servo control means and said tracking servocontrol means so that said focus servo control means and said trackingservo control means perform defect period processing when a result ofthe monitoring by said monitoring means indicates said defect period;and post-defect period processing control means for controlling saidfocus servo control means and said tracking servo control means so thatsaid focus servo control means and said tracking servo control meansperform post-defect period processing when a result of the monitoring bysaid monitoring means indicates the end of said defect period.
 2. Aplayback apparatus as claimed in claim 1, wherein said defect periodprocessing control means controls said focus servo control means andsaid tracking servo control means so that said focus error signal orsaid tracking error signal of said optical pickup is held at apredetermined value.
 3. A playback apparatus as claimed in claim 1,wherein said post-defect period processing control means controls saidfocus servo control means and said tracking servo control means so thatservo operation of said optical pickup is sped up.
 4. A playbackapparatus as claimed in claim 1, wherein when said monitoring meansdetects the start of said defect period during said post-defect periodprocessing performed under control of said post-defect period processingcontrol means, said post-defect period processing control means stopssaid post-defect period processing, and said defect period processingcontrol means starts said defect period processing.
 5. A playback methodfor a playback apparatus, said playback apparatus reproducing datarecorded on a disk medium by using an optical pickup, said playbackmethod comprising: an RF signal generating step for generating an RFsignal on the basis of an analog signal outputted by said opticalpickup; a data signal generating step for generating a data signal bybinarizing said RF signal; a defect signal generating step forgenerating a defect signal for indicating a defect on said disk mediumon the basis of said RF signal; a focus error signal generating step forgenerating a focus error signal on the basis of said analog signaloutputted by said optical pickup; a focus servo control step forcontrolling a focus servo of said optical pickup in response to saidfocus error signal; a tracking error signal generating step forgenerating a tracking error signal on the basis of said analog signaloutputted by said optical pickup; a tracking servo control step forcontrolling a tracking servo of said optical pickup in response to saidtracking error signal; a monitoring step for monitoring said defectsignal and thereby detecting a start and an end of a defect period; adefect period processing control step for controlling processing of saidfocus servo control step and processing of said tracking servo controlstep so that defect period processing is performed when a result of themonitoring by processing of said monitoring step indicates said defectperiod; and a post-defect period processing control step for controllingthe processing of said focus servo control step and the processing ofsaid tracking servo control step so that post-defect period processingis performed when a result of the monitoring by the processing of saidmonitoring step indicates the end of said defect period.
 6. A recordingmedium for recording a computer readable playback program forreproducing data recorded on a disk medium by using an optical pickup,said program comprising: an RF signal generating step for generating anRF signal on the basis of an analog signal outputted by said opticalpickup; a data signal generating step for generating a data signal bybinarizing said RF signal; a defect signal generating step forgenerating a defect signal for indicating a defect on said disk mediumon the basis of said RF signal; a focus error signal generating step forgenerating a focus error signal on the basis of said analog signaloutputted by said optical pickup; a focus servo control step forcontrolling a focus servo of said optical pickup in response to saidfocus error signal; a tracking error signal generating step forgenerating a tracking error signal on the basis of said analog signaloutputted by said optical pickup; a tracking servo control step forcontrolling a tracking servo of said optical pickup in response to saidtracking error signal; a monitoring step for monitoring said defectsignal and thereby detecting a start and an end of a defect period; adefect period processing control step for controlling processing of saidfocus servo control step and processing of said tracking servo controlstep so that defect period processing is performed when a result of themonitoring by processing of said monitoring step indicates said defectperiod; and a post-defect period processing control step for controllingthe processing of said focus servo control step and the processing ofsaid tracking servo control step so that post-defect period processingis performed when a result of the monitoring by the processing of saidmonitoring step indicates the end of said defect period.